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"I can only surmise that many USAF Generals must have bitterly regretted the decision to scrap the Rainbow. Neither the RB-17 or the RB-29 used on early overflights of Russia possessed anything like the performance of the Rainbow and if the aircraft had been developed it could have roamed freely over vast tracts of Eastern Europe and Russia for many years with virtual impunity.
The use by the USA of converted bomber aircraft with comparitively modest performance, to perform reconnaissance duties in the early cold war years ended up costing the lives of many brave men."
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Republic XF-12 Rainbow - Wikipedia, the free encyclopedia
Republic XR-12 Rainbow. The Republic XR-12 Rainbow is in many peoples opinion one of the most graceful aircraft of all time, as well as being probably the most ...
Republic XR-12 Rainbow
The Republic XR-12 Rainbow is in many peoples opinion one of the most graceful aircraft of all time, as well as being probably the most streamlined piston-engined aircraft every built. The Rainbow was built to an exacting 1943 USAAF requirement for a purpose-built reconnaissance aircraft. The requirement specification was drawn up by the photographic Section of the Air Technical Service from recommendations made by Colonel Elliot Roosevelt and called for a very long range, high speed aircraft specifically tailored for photographic reconnaissance. Republic's chief designer, Alexander Kartveli, felt that to achieve the required altitude and speed, over 40,000ft and 400mph, four large pistion engines would be required and selected the Pratt & Whitney R-4360 Wasp Major radial of 3,500hp. The aircraft eventually proved capable of maintaining Mach.8 at 40,000ft.
With a beautifully streamlined body and an elegant 129ft wing, the aircraft was designed from the outset to carry, not just any combination of cameras in three special camera compartments, but also a complete dark room for developing the photographs in flight. The first prototype flew on 4 Feb 46 and, although the aircraft was extensively tested, the end of the Second World War meant that the urgency was lost from the programme and the second aircraft did not fly until 12 Aug 47. Unfortunately the second aircraft was badly damaged when its number two engine exploded on a test flight. In addition, a 'Peace Dividend' was needed to appease the usual 'bean-counters' and despite the Cold War beginning to settle in, the short-sighted individuals in charge of the USAF could see no need for a specialised reconnaissance aircraft and the requirement was withdrawn.
Flight testing of the Rainbows continued for some time to assess the aircraft's suitability as a high-speed transatlantic airliner for Pan-Am. However, after the USAF cancelled the military requirement for 20 aircraft, Republic could not afford to produce an affordable airliner and the these two superb aircraft were eventually broken up for scrap. As the Cold War built up and a variety of converted bombers were hastely pressed into reconnaissance duties, I can only surmise that many USAF Generals must have bitterly regretted the decision to scrap the Rainbow. Neither the RB-17 or the RB-29 used on early overflights of Russia possessed anything like the performance of the Rainbow and if the aircraft had been developed it could have roamed freely over vast tracts of Eastern Europe and Russia for many years with virtual impunity.
The use by the USA of converted bomber aircraft with comparitively modest performance, to perform reconnaissance duties in the early cold war years ended up costing the lives of many brave men.
Artist Proof from Limited Edition of 250 S/N by the Artist Image Size: 17.5" x 10.5" Paper Size: 22" x 17" Plane Type: Republic XR-12 In the final years of World War ...
Republic XR-12 Rainbow
Product Description
Artist Proof from Limited Edition of 250
S/N by the Artist
Image Size: 17.5" x 10.5"
Paper Size: 22" x 17"
Plane Type: Republic XR-12
In the final years of World War II, the U.S. Army Air Forces identified the need for a long-range photo reconnaissance aircraft to survey the Pacific Theater of Operations, but that mission became obsolete at War's end. Built to meet that requirement was the sleek and graceful Republic XR-12 which could reach speeds in excess of 450 mph in level flight. A commercial airliner version named the Rainbow offered near-jet-like performance for the world's airlines, but the XR-12 never entered production and airlines bought war-surplus transports instead. Still the world's fastest multi-engine piston-powered aircraft, the Republic XR-12 offered the world a tantalizing glimpse of the future in the heady years at the very beginning of the jet age.
Model Features: 56 resin parts + Vac-formed canopy & Decal Span 546 mm. x. Length 397 mm
In 1943, the USAAF had an urgent need to fly photo-reconnaissance missions over the Pacific Theater to identify Japanese positions and movements. But its airfields were far too distant for the medium-range planes to make the round trip. Its only recourse was to issue a request for a new long-range, high altitude reconnaissance plane capable of the long-endurance missions the Pacific War required. In March 1944, Republic Aircraft responded to the USAAF by proposing to modify its experimental civilian RC-2 transport to the specifications. The proposal was accepted and Republic received an order for two prototypes which designated XF-12. Its competitor was the Hughes XF-11. While the Rainbow was under development, the USAAF converted several B-29 bombers into recon aircraft, reclassifying them as F-13s. Even after the war, Republic continued to develop the Rainbow, changing its designation from the XF-12 ("F" stood for "Foto") to the XR-12 ("R" for "Reconnaissance"). The first XR-12 made its maiden flight in February 1947. Its performance was up to expectations, making it the fastest four piston-engine aircraft flying at the time. Development of the two prototypes continued until 1948 when the USAF canceled the program, choosing the newer RB-29 and RB-50 instead.
Type:Purpose:Span:Length:Height:Engine:Max.speed:Crew:Armament:long-range photo-reconnaissance aircraftOriginally to envision as a civilian airliner, and modified to meet military's photo-reconnaissance airplane requirement129ft.2in.93ft.10in.28ft.9in.4x Pratt & Whitney R-4360-31 radials460 mph7None
XR-12 / XF-12 Originally envisioned as a transatlantic passenger plane for Pan ... the whole postwar structure of aircraft markets might have been altered, with Republic ...
XR-12 / XF-12
Originally envisioned as a transatlantic passenger plane for Pan American World Airways, the Rainbow lost out in the commercial market because of its small forty-four-passenger capacity. The beautifully streamlinedRainbow had aesthetically appealing lines, and as the wartime XF-12 (later XR-12) it was converted into a flying photographic laboratory, suffering the ordinary development problems, including an engine fire and subsequent crash.
The advent of World War II brought into focus the critical importance of timely and accurate intelligence gathering. Field commanders needed the ability to make pivotal strategic decisions leading to successful campaigns. Thus the need arose for an aircraft specifically designed for the photo-reconnaissance mission providing pre-strike photo interpretation of potential targets and the post-strike analysis of their subsequent destruction.
Republic Aviation’s F-12 was born out of the same competition as the Hughes XF-11 in response to the pressing need for speed, ceiling and range in a photo-reconnaissance aircraft. The first flight of the XF-12 was made on Feb. 4, 1946, which demonstrated the capability of operating at 45,000 feet at a speed of 470 mph over a range of 4,500 miles.When the XF-12 was modified with increased "all weather" equipment and outfitted with a new power plant capable of providing short bursts of extreme power, it suddenly assumed tremendous importance in the eyes of both the U.S. Air Force and the State Department. As a potent intelligence weapon, the XF-12 had the ability to obtain photographs both in daylight and under conditions of restricted visibility and at high altitudes over long ranges and with great speed. Operating from northern bases (Alaska and Canada), this "flying photo laboratory" was capable of mapping broad stretches of territory in the Arctic regions performing reconnaissance with near-invulnerability.Low-drag was a primary consideration throughout the design of the XF-12. Many of its features were taken directly from Republic’s considerable experience with fighter plane design. In a extremely rare case of design direction absolutely no compromise with aerodynamics was made in the shape of its fuselage. The long, pointed nose of the design virtually prohibited flow separation.The XF-12 carried a variety of photographic equipment, including complete dark room facilities to permit the development and printing of films in flight. It contained three separate photographic compartments and a large hold in the belly accommodated 18 high-intensity photo-flash bulbs to permit night photography.The mission called "Operation Bird's-eye" was conceived to demonstrate the newly-designated XR-12’s ultimate photo capabilities. On Sept. 1, 1948, the second XR-12 lifted off from Air Force Flight Test Center at Muroc, Calif., and climbed westward to gain altitude over the Pacific Ocean. Upon reaching its 40,000 foot cruising altitude, the XR-12 headed eastward and began photographing its entire route of flight over the entire United States. The crew shot a continuous 325 foot long strip of film composed of 390 individual photos covering a 490-mile-wide field of vision. The aircraft landed at Mitchel field at Garden City, Long Island, N.Y., completing a flight lasting six hours and 55 minutes.The record shattering flight was featured in the Nov. 29, 1948, issue of Life magazine and the actual filmstrip went on exhibit at the 1948 Air Force Association Convention in New York City.At the time this record was made, the Air Force had already canceled the entire XF-12 program. The primary reason for its demise was the availability of both B-29 and B-50 types to meet the long-range photo-reconnaissance requirement until the far more capable RB-47 was brought into service. Had the Rainbow been available in 1944, it almost inevitably would have been ordered in quantity, and the whole postwar structure of aircraft markets might have been altered, with Republic building follow-on airliners. As it was, the Rainbow disappeared into oblivion, despite its graceful lines and high performance.
- User rating: 4.7/5 ·
- By Mike Machat ·
- Hardcover ·
- 13 reviews
Amazon.com: World's Fastest Four-Engine Piston-Powered Aircraft: Story of the Republic XR-12Rainbow (9781580071635): Mike Machat: Books
Still the fastest multi-engine piston aircraft ever flown, the Republic XR-12 and its competitor, the Hughes XF-11, were well ahead of their time in 1946. Envisioned as a long-range photo-reconnaissance aircraft with a top speed of more than 450 mph, the Republic XR-12 also offered near jet-like performance for the world's airlines with a 44-passenger commercial version named the Rainbow. Using original Republic photos, data, and artwork, the author reveals never-before-published information about the Rainbow airliner. While the clear emphasis of this book is on the Republic airplane, the Hughes XF-11 is also covered and compared in its role as a twin-engine competitor to the more advanced four-engine Republic airplane. Although the XR-12 and XF-11 were among the most elegant-looking aircraft ever built, the Rainbow was considered to be Republic chief designer Alexander Kartveli's ultimate masterpiece. Conversely, the more cantankerous XF-11 almost took the life of its designer and chief test pilot, Howard Hughes.
The Republic XR-12 Rainbow Reconnaissance Aircraft The 'might have been' Rainbow was beautiful, fast, and finished before it began production
n a long career testing everything from the P-47 Thunderbolt to the F-105 Thunderchief, celebrated test pilot Lin Hendrix regretted few experiences more than parachuting from the sleek, silvery Republic XR-12 Rainbow and abandoning the aircraft to the inexorable force of gravity.“It was so beautiful and so promising,” Hendrix said in an interview in the 1980s. “It was such a pity to lose it.”From some angles the XR-12 (initially, the XF-12) looked like a bullet in motion, even when it was sitting still. It may have been the most eye-pleasing propeller aircraft ever built. To some minds, it was not just a U.S. Army Air Forces (AAF) reconnaissance aircraft but also a potential airliner for a possibly lucrative post-World War II aviation market.Instead, the XR-12 ended up being a “might have been,” its promise never fulfilled. In later years, single-mission reconnaissance aircraft ranging from the SR-71 Blackbird to the RQ-1A Predator demonstrated that Hendrix, test pilot Lowry Brabham and designer Alexander Kartveli were far from wrong: They were simply ahead of their time.
The XR-12 design incorporated four massive 3,500-horsepower, 28-cylinder Pratt & Whitney R-4360-37 Wasp Major engines, the epitome of piston engine technology. Photo courtesy of the Robert F. Dorr CollectionThe XR-12 (designated XF-12 prior to June 5, 1948) was built to meet a 1943 AAF requirement that reflected the infatuation of Col. Elliott Roosevelt with the “convoy fighter” – a flying battleship, bristling with guns, that would accompany Allied bombers to Berlin and Tokyo. When it became clear that the escort mission could be handled by the Merlin engine-powered P-51 Mustang, President Franklin D. Roosevelt’s son helped change the purpose of the plane he wanted to long-range reconnaissance.Fortunately, a requirement for such an aircraft was readily at hand. The AAF had determined that it needed a high-speed, long-range reconnaissance aircraft for operations in the Pacific (it did not yet have experience with the F-13 Superfortress, the reconnaissance version of the B-29 and the next plane in the “F” for “foto” series). The AAF’s Air Technical Services Command at Wright Field, Ohio, put out what today would be called a request for proposals.Reconnaissance Rainbow
To complete with an aircraft being developed by Howard Hughes, Republic’s master designer Kartveli sought to attain the prescribed speed and altitude – the so-called “four-four” goal of 400 miles per hour and 40,000 feet – by streamlining the colossal 3,500-horsepower, 28-cylinder Pratt & Whitney R-4360-37 Wasp Major engine, versions of which were used on the B-36 Peacemaker and B-50 Superfortress bombers. Kartveli’s team positioned the engines’ air-cooling inlets in the wing leading edge rather than in the nacelles. The engines incorporated high-speed blowers. An exhaust-driven General Electric turbo-supercharger was located in the rear of each nacelle, gathering thrust of up to one-third of the original horsepower. Each engine drove a 16-foot, four-bladed Curtiss propeller with a bullet-like pointed hub. Other aerodynamic tweaks, plus a carefully designed mid-wing configuration, produced an aircraft with remarkably little drag. In March 1944, the AAF ordered two prototypes (serials 44-91002/91003), but the war was already won when the first of these rolled out at Farmingdale, Long Island, in December 1945.
The frontal view of the Republic XR-12 provides a good view of the mid-wing design that lowered drag. The aircraft set a new cross country record by averaging 426 mph between New York and Wright Field, Ohio. Photo courtesy of the Robert F. Dorr CollectionThe first ship completed its maiden flight on Feb. 7, 1946 with Brabham at the controls. A proof-of-concept airframe, it carried no mission cameras. The second aircraft, which flew on Aug. 12, 1947 with Hendrix as pilot, was a true reconnaissance aircraft, capable of taking photographs and of furnishing all required film-processing and interpretive facilities in flight, a capability never matched by any other platform during the decades when cameras used film. One proposed configuration had eleven crewmembers with spacious work facilities in the fuselage behind the single pilot.In May 1946, the Rainbow set a new cross-country speed record for four-engined aircraft, covering 576 miles between New York and Wright Field at 426 miles per hour. A Lockheed Constellation had held the previous record of 375 miles per hour.On Nov. 4, 1948, this mission-equipped second ship experienced an explosion in its number two engine nacelle, which gave Hendrix and the others in his three-man crew no choice but to hit the silk. Flight testing of ship number one was suspended. <continued in original article>
XF-12 Rainbow Role Strategic reconnaissance Manufacturer Republic Aviation Designer Alexander Kartveli First flight 4 February 1946 Introduction December 1945 Retired June 1952 Status Cancelled Primary user United States Army Air Force Number built 2 Unit cost $1.25 Million (1946 Dollars)
[edit]DevelopmentContents
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XF-12 Rainbow c. 1946[edit]Design
XF-12 Rainbow in flight c. 1947[edit]Operational history[edit]Specifications (XF-12)
- Length: 93 ft 9 in (RC-2 version 98 ft 9 in) (28.56 m)
- Wingspan : 129 ft 2 in (RC-2 version 129 ft 2 in) (39.37 m)
- Height: 28 ft 1 in (RC-2 version 29 ft 11 in) (8.55 m)
- Wing area: 1,640 ft² (RC-2 version 1,640 ft²) (152.36 m²)
- Empty weight : 65,000 lb (RC-2 version 67,000 lb) (29,483 kg)
- Loaded weight: 101,400 lb (RC-2 version 114,200 lb) (45,994 kg)
- Max. takeoff weight : 101,400 lb (RC-2 version 114,200 lb) (45,994 kg)
- Powerplant : 4 × Pratt & Whitney R-4360-31 Radial engine, 3,250 hp (2,423 kW each) each
- Maximum speed : 470+ mph (RC-2 version 450 mph) (756 km/h)
- Range : 4,500 miles (RC-2 version 4,100 miles) (7,242 km)
- Service ceiling : 45,000 ft (RC-2 version 40,000 ft) (13,716 m)
- Rate of climb : 5,000+ ft/min (RC-2 version 5,000+ ft/min) (1,524 m/min)
- Wing loading : 61.83lb/ft² (301.9 kg/m²)
- Power/mass : hp/lb (kW/kg)
Aircraft of comparable role, configuration and era
Related lists
[edit]References
Notes
- ^ Machat 1994, p. 12.
- ^ Aviation Week, 10 November 1947
- ^ Machat 1994, p. 16.
- ^ Machat 1994, p. 14.
- ^ Machat 1994, p. 10.
- ^ Machat 1994, p. 50.
- ^ Machat 1994, p. 51.
- ^ "Seven Airmen Dead in Eglin Plane Crashes". Playground News, Fort Walton, Florida, 11 November 1948, Volume 3, Number 41, p. 1.
- ^ Machat 1994, pp. 50–51.
- ^ Machat 1994, p. 9.
- Aviation Week , 10 November 1947.
- Life magazine , November 1948.
- Machat, Mike. "Somewhere, Under a Rainbow." Wings Volume 24, No. 2, April 1994.
- Marrett, George. "Flights Into the Future." Wings Volume 35, No. 12, December 2005.
- "First with the Fastest." Popular Science, July 1946, pp. 74-78.
The Republic XF-12 Rainbow was an American four-engine, all-metal prototype reconnaissance aircraft designed by theRepublic Aviation Company in the late 1940s. Like most large aircraft of the era, it used radial engines—in this case, thePratt & Whitney R-4360 "Wasp Major." The aircraft was designed with maximum aerodynamic efficiency in mind. The XF-12 was referred to as an aircraft that was "flying on all fours" meaning: four engines, 400 mph cruise, 4,000 mile range, at 40,000 feet.[1]Although highly innovative, the postwar XF-12 Rainbow was fated to compete against more modern jet engine technology and was not to enter production.The original proposal for the aircraft, delivered in late 1943, came from the USAAC Air Technical Service Command, stationed at Wright Field. The proposal was for a reconnaissance aircraft which included a requirement for speed (400 mph), ceiling (40,000 ft) and range (4,000 nm). Its primary objective was for high-speed overflights of the Japanese homeland and key enemy installations. During World War II, due to the extended range requirements of operating in the Pacific, existing fighters and bombers were being used for missions for which they were never intended. The need existed for an aircraft specifically designed for the photo-reconnaissance mission. The aircraft required adequate speed, range and altitude capabilities for its missions to be successful.In August 1943, US President Franklin D. Roosevelt's son, Colonel Elliot Roosevelt, commander of the F-5 (modified P-38) "recon" unit, recommended the acquisition of a dedicated high-performance photo reconnaissance aircraft, capable of providing pre-strike target acquisition and photo interpretation. Followed by additional overflights to provide post-strike analysis of their subsequent destruction, this would give commanders the ability to make pivotal strategic decisions and set up subsequent raids. The XF-12 was Republic Aviation's attempt to meet those goals. Its primary competition during this time was the Hughes XF-11. Both were introduced at the same time, and both were powered by the new P&W R-4360. The XF-12's first flight was made on 4 February 1946. During the XF-12's subsequent flight testing and development period, it demonstrated the capability of operating at 45,000 ft, at a speed of 470 mph, over a range of 4,500 miles so it met and exceeded the design goals for which it had been designed. Neither the XF-11 or the XF-12 was purchased in any quantity by the Air Force (two each), as their need evaporated after hostilities ended in World War II. [2]When the XF-12 was modified with increased "all weather" equipment and outfitted with its new engines capable of providing short bursts of extra power, it suddenly assumed tremendous importance in the eyes of both the U.S. Air Force and the State Department. As a potent intelligence weapon, the XF-12 had the ability to obtain photographs both in daylight and under conditions of restricted visibility at high altitudes over long ranges and with great speed. In theory, operating from northern bases (Alaska and Canada), this "flying photo laboratory" was capable of mapping broad stretches of territory in the Arctic regions performing reconnaissance with near-invulnerability. [3]Low drag was a primary consideration throughout the design of the XF-12. Many of its features were taken directly from Republic’s considerable experience with fighter plane design. In an extremely rare case of design direction, absolutely no compromise with aerodynamics was made in the shape of its fuselage. Aviation Week was quoted as saying "the sharp nose and cylindrical cigar shape of the XF-12 fulfills a designer's dream of a no compromise design with aerodynamic considerations."To fulfill its reconnaissance role, the XF-12 contained three separate photographic compartments aft of the wing. One vertical, one split vertical, and one trimetrogon each using a six inch Fairchild K-17 camera. For night reconnaissance missions, the XF-12 had a large hold in the belly which accommodated 18 high-intensity photo-flash bombs; these were ejected over the target area. All of the bays were equipped with electrically operated, inward retracting doors (again designed for maximum aerodynamic cleanliness). The camera lenses were electrically heated to eliminate distortion. All of this combined to allow full photo operations during high speed flights. The XF-12 also carried a variety of photographic equipment, including complete darkroom facilities to permit the development and printing of films in flight. This was augmented by adjustable storage racks, able to handle any size film containers and additional photo equipment. This allowed the Army Intelligence units to have immediate access to the intelligence the aircraft was able to collect, with no delay in processing.[4]The Rainbow featured a wing of straight taper with squared tips and high aspect ratio for maximum efficiency. The engines featured a sliding cowl arrangement to facilitate cooling airflow instead of the normal cowl flaps, which caused too much drag. At the front of the cowls, the engines were also fitted with a two stage "impeller fan" directly behind thepropeller hub and prop spinner. This allowed the engines to be tightly cowled for aerodynamic efficiency, but still provide the cooling airflow the engines required. When the sliding cowl ring was closed (during flight), the air used for cooling the engine was ducted through the nacelle to the rear exhaust orifice for a net thrust gain, as opposed to the usual cooling drag penalty.All of the air for the engine intakes, oil coolers and intercoolers was drawn through the front of each wing between the inboard and outboard engines. This allowed less drag than with individual intakes for each component. In addition, because the air was taken from a high-pressure area at the front of the wing, this provided a "ram air" benefit for increased power at high speeds, and more effective cooling of the oil and intercoolers. The intake portion of the wing comprised 25% of the total wingspan. They were extensively wind tunnel tested for intake efficiency and inlet contour efficiency. This cooling air, after being utilized, was ducted toward the rear of the nacelle, to provide additional net thrust. The entire engine nacelle was the length of a P-47 Thunderbolt (also built by Republic). Each engine featured twin General Electric turbochargers, situated at the aft end of the nacelle.All of the exhaust from the P&W R-4360 was ducted straight out of the back of the nacelles. This provided additional thrust. Research showed that approx 250 equivalent horsepower was generated by each engine exhaust during high speed cruise at 40,000 ft.[5]The original design of the XF-12 called for contra-rotating propellers, similar to those used on the original XF-11. However due to the added complexity and reliability issues, the propellers were never installed. They would have been twin three-bladed propellers (rotating in opposite directions). As it was, the aircraft used standard four-bladed Curtiss Electric propellers for all flights. [6]The first prototype was damaged in landing on 10 July 1947. The aircraft was undergoing maximum landing weight tests. During one particularly hard landing, the right main gear was severed at the engine nacelle. The aircraft bounced hard, and staggered back into the air. The test pilot was able to maintain control, and climb to a safe altitude. He continued to fly the aircraft to burn off excess fuel, to both make the aircraft lighter and lessen the chance of fire. Once excess fuel was burned off, the pilot landed on the left main gear and the nose wheel. The pilot touched down, and while keeping the right wing up, scrubbed off as much speed as possible before it touched down. During the incident the aircraft suffered significant damage. The right wing spar was cracked, and the #3 and #4 engines and props needed to be replaced due to the ground contact. The aircraft was repaired by Republic, and later returned to service. [7]The only external difference between the first and second prototypes was the addition of cooling gills on the upper engine cowlings. Internally, the second prototype was far more "finished." This included its full operational reconnaissance equipment suite, to allow for further testing. [8]The XF-12 was later re-designated XR-12, when the Army Air Force separated from the Army and became the U.S. Air Force.The most successful part of the XF-12 flight history is "Operation Birds Eye." The mission was conceived to demonstrate the newly designated XF-12’s ultimate photo capabilities. On 1 September 1948 the second prototype XF-12 departed Air Force Flight Test Center at Muroc, California, and climbed westward to gain altitude over the Pacific Ocean. Upon reaching its 40,000 ft cruising altitude, the XF-12 headed eastward and began photographing its entire flight path over the United States. The crew shot a continuous 325 foot-long strip of film composed of 390 individual photos covering a 490-mile-wide field of vision. The aircraft landed at Mitchel Field at Garden City, Long Island, New York, completing a flight lasting six hours and 55 minutes at 361 mph average speed. The record-shattering flight was featured in the 29 November 1948 issue of Life magazine and the actual filmstrip went on exhibit at the 1948 Air Force Association Convention in New York. [1]At the time this record flight was made, the Air Force had already canceled the entire XF-12 program. The primary reason for its demise was the availability of both B-29 and B-50types to meet the long-range photo-reconnaissance requirement until the far more capable RB-47 was brought into service. The B-29 and B-50 gave the Air Force less costly "off the shelf" options. [8]Republic had intended to also build an airline version of the aircraft to be known as the RC-2. This variant was supposed to be a "stretched" version of the XF-12, growing in length from 93 ft 9 in to 98 ft 9 in, with the addition of a fuselage "plug" in front of the wing. Also the complex Plexiglas nose section was supposed to be replaced with a solid metal nose with a bifurcated windshield. Fuel capacity would have been increased, and more powerful (at lower altitude) P&W R-4360-59s would have been substituted in place of the P&W R-4360-31s on the Air Force version. The engines also would have only had one General Electric turbo supercharger each, instead of the dual arrangement on the Air Force model. The aircraft would be lavishly appointed for the 46 passengers and seven crew. It would have been fully pressurized to sea level, air conditioned, with an electric galley providing hot meals and with an inflight lounge. It would have had the ability to cruise above the weather at 435 mph at 40,000 feet. No versions of this aircraft were ever built.[9]Without an order from the Air Force to offset the cost for development and tooling, the cost of building the civilian airliners went up exponentially. As a result, the two airlines (American Airlines and Pan-Am) that had originally placed tentative purchase orders, both cancelled due to the additional unit cost. Economically, the RC-2 wasn't as feasible as other designs available at the time, such as the Lockheed Constellation and the Douglas DC-6. Both of those aircraft could carry more people, at a lower cost per mile. In addition, after the hostilities ended in World War II, there were large collections of surplus military transports available for purchase, such as the C-54 Skymaster. These former transport aircraft lent themselves to be readily converted to airline service at a fraction of the cost of buying new aircraft. Without additional orders, Republic cancelled all further plans to build not only the XF-12 but also the RC-2, leaving just the two original prototypes.On 7 November 1948, prototype number two, 44-91003, crashed at 1300 hrs. while returning to Eglin Air Force Base, Florida. The number 2 (port inner) engine exploded as the aircraft was returning from a photographic suitability test flight. The pilot was unable to maintain control due to violent buffeting, and he ordered the crew to bail out. Five of the seven crew escaped safely, including pilot Lynn Hendrix, rescued by Eglin crash boats and helicopters. Airframe impacted two miles south of the base, in the Choctawhatchee Bay. Sgt. Vernon B. Palmer and M/Sgt. Victor C. Riberdy were killed. [10] The first prototype, which returned to service in 1948, continued the flight testing and development phase. After the Air Force declined to order any additional aircraft, and with the loss of the second prototype, the flight testing period wound down. In June 1952 the first prototype, 44-91002, was retired (having flown just 117 additional hours from 1949 to 1952), was stricken from the Air Force inventory and ended up as a target on the Aberdeen Proving Ground, Maryland.[11]Had the XF-12 Rainbow been available in 1944, it almost inevitably would have been ordered in quantity, and along with its civilian counterpart, the whole postwar structure of aircraft markets might have been altered. As it was, the XF-12 disappeared into oblivion, despite its graceful lines and high performance. According to Machat, the Rainbow remains the ultimate expression of multi-engine, piston-powered aircraft design. Its high speed, near-perfect streamlined form, and neatly cowled engines make it a design classic, often unappreciated, and not very well known. The XF-12 was the fastest four engine pure piston-powered aircraft of its day, and the only such ever to exceed 450 mph in level flight. [12]General characteristicsPerformance
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